sparse-revlog: add a `index_get_start` function in C
We are about to implement a native version of `slicechunktodensity`. For
clarity, we introduce the helper functions first. This new function provides
an efficient way to retrieve some of the information needed by
`slicechunktodensity`.
--- a/mercurial/cext/revlog.c Fri Nov 23 06:32:32 2018 +0100
+++ b/mercurial/cext/revlog.c Tue Nov 20 14:49:18 2018 +0000
@@ -185,6 +185,40 @@
return 0;
}
+static inline int64_t index_get_start(indexObject *self, Py_ssize_t rev)
+{
+ uint64_t offset;
+ if (rev >= self->length) {
+ PyObject *tuple;
+ PyObject *pylong;
+ PY_LONG_LONG tmp;
+ tuple = PyList_GET_ITEM(self->added, rev - self->length);
+ pylong = PyTuple_GET_ITEM(tuple, 0);
+ tmp = PyLong_AsLongLong(pylong);
+ if (tmp == -1 && PyErr_Occurred()) {
+ return -1;
+ }
+ if (tmp < 0) {
+ PyErr_Format(PyExc_OverflowError,
+ "revlog entry size out of bound (%lld)",
+ (long long)tmp);
+ return -1;
+ }
+ offset = (uint64_t)tmp;
+ } else {
+ const char *data = index_deref(self, rev);
+ offset = getbe32(data + 4);
+ if (rev == 0) {
+ /* mask out version number for the first entry */
+ offset &= 0xFFFF;
+ } else {
+ uint32_t offset_high = getbe32(data);
+ offset |= ((uint64_t)offset_high) << 32;
+ }
+ }
+ return (int64_t)(offset >> 16);
+}
+
/*
* RevlogNG format (all in big endian, data may be inlined):
* 6 bytes: offset